This invention pertains to apparatus for use in applying solder to internal openings of can body side seams.
In the prior art side seam soldering apparatus a fairly well established practice has been to conduct successive can bodies, to be side seam soldered internally, along an extension of a stub horn, and over a rotary solder roll but out of contact therewith. In such arrangements the stub horn extension is customarily provided with a series of vertically displaceable "solder irons" engageable at their lower ends with the solder roll to receive heat and solder therefrom. A leading edge of each can accordingly engages a bevelled portion of each of the solder irons to raise them sufficiently to allow each inside of a side seam to pass beneath the irons whereby they can transfer heat and solder "picked up" from the roll to a wide internal band along the seam.
The need for applying internal side seam soldering, whether by the means briefly described or some other technique, exists to prevent can contents from contactng raw steel edges which might adversely affect taste or texture. Moreover, in addition to the possibility of weakening a thin-walled container by reason of a chemical reaction with uncoated inner metal edges, inside seam soldering is often highly desirable in order to avoid disturbing exterior lithography on the can bodies. A difficulty associated with known inside seam soldering approaches has been that excessive solder has been applied in bands considerably wider than required for coating the seams. No practical way exists of removing the excess solder so that any lead contamination tendency may be increased and container cost is also increased.
U.S. patents pertaining to side seam soldering of cans which may be referred to for background, if desired, include for instance, Nos. 3,000,338; 3,056,368; 3,190,526; and 3,255,856.